The Sierra Madre Occidental runs mainly through Mexico. This major mountain system extends from near the Arizona–Sonora border southeastward through western and northwestern Mexico, broadly paralleling the Pacific coast.
The range crosses or borders numerous Mexican states, including Sonora, Chihuahua, Sinaloa, Durango, Zacatecas, Nayarit, Jalisco and Aguascalientes. It eventually transitions toward the Sierra Madre del Sur and the Trans-Mexican Volcanic Belt. Its name translates from Spanish as “Western Mother Mountain Range,” distinguishing it from the Sierra Madre Oriental to Mexico’s east.
The Sierra Madre Occidental is famous for high plateaus cut by deep river canyons. Copper Canyon, or Barranca del Cobre, is the best-known example. These mountains also support extensive pine–oak forests and important watersheds in a region surrounded by deserts and dry forests.
The range is sometimes confused with the Sierra Madre Oriental because both are large Mexican systems. Colombia, Peru and Chile have major mountain landscapes of their own, especially within the Andes, but none contains the Sierra Madre Occidental. Mexico is therefore the single canonical answer for this question.